Suddenly Lost data after this 'index not found exception'

Hi

Today i have faced strange issue, After i am getting cluster alert for red, I have investigated on the particular Node which one is down.

In this node we have 3 shards ,each contains 400 - 500 GB Data.After I got a following exception ,i checked there is data loss and lost every files.

Caused by: org.elasticsearch.index.gateway.IndexShardGatewayRecoveryException: [xindex][0] shard allocated for local recovery (post api), should exist, but doesn't, current files: []
Caused by: org.apache.lucene.index.IndexNotFoundException: no segments* file found in store(least_used[rate_limited(mmapfs(/disk01/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0), rate_limited(mmapfs(/disk02/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0), rate_limited(mmapfs(/disk03/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0), rate_limited(mmapfs(/disk04/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0), rate_limited(mmapfs(/disk05/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0), rate_limited(mmapfs(/disk06/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0), rate_limited(mmapfs(/disk07/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0), rate_limited(mmapfs(/disk08/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0), rate_limited(mmapfs(/disk09/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0), rate_limited(mmapfs(/disk10/ESData/elasticsearch/nodes/0/indices/xindex/0/index), type=MERGE, rate=20.0)]): files: []

Can you please explain what is the cause for this exception and how can we override this issues.

Thanks
Moni